A comparison of shear bond strength and debonding characteristics of conventional, moisture-insensitive, and self-etching primers in vitro.

Bond failure is often attributed to moisture contamination. To overcome this commonly encountered problem, materials have been developed that are hydrophilic and that are believed to offer better bond strength in moisture-contaminated environment. Shear bond strength was compared among three materials: conventional Transbond XT primer (3M Unitek), moisture-insensitive primer (MIP, 3M Unitek), and self-etch primer (Transbond plus, 3M Unitek). Bond strength was tested under laboratory conditions with brackets bonded on both dry enamel and enamel contaminated with natural saliva. Self-etch primer showed maximum bond strength under both dry and wet conditions. Conventional primer was comparable with the former under dry conditions but did not offer clinically adequate bond strength in cases of moisture contamination. Both MIP and self-etch primer showed adequate bond strength superior to that of conventional primer in case of moisture contamination. All primers showed typical debonding characteristics of separation at the bracket-adhesive interface or within the adhesive itself, with the exception of the conventional primer used with moisture-contaminated enamel.